let _Vue = null
export default class VueRouter {
    static install (Vue) {
        // 1. 判断当前插件是否已经安装
        if (VueRouter.install.installed) {
            return
        }
        VueRouter.install.installed = true
        // 2. 把Vue构造函数记录到全局变量
        _Vue = Vue
        // 3. 把创建Vue实例时候传入的router对象注入到Vue实例上
        // _Vue.prototype.$router = this.$options.router // this指向当前函数
        // 混入
        _Vue.mixin({
            beforeCreate () {
                if (this.$options.router) {
                    _Vue.prototype.$router = this.$options.router
                    this.$options.router.init()
                }
            }
        })
    }

    constructor (options) {
        this.options = options
        this.routeMap = {}
        let newHash = window.location.hash
        let path = ''
        if (newHash === '#/' || newHash === '') {
            path = '/'
            this.getHashUrl(this.options.base)
        } else {
            path = newHash.substr(1)
        }
        this.data = _Vue.observable({
            current: path
        })
    }

    init () {
        this.createRouteMap()
        this.initComponents(_Vue)
        this.initEvent()
    }

    getHashUrl (path) {
        let i = window.location.href.indexOf('#')
        window.location.replace(
            window.location.href.slice(0, i >= 0 ? i : 0) + '#' + path
        )
    }

    createRouteMap () {
        // 遍历所有的路由规则， 把路由规则解析成键值对的形式 存储到routeMap中
        this.options.routes.forEach(route => {
            this.routeMap[route.path] = route.component
        })
    }

    initComponents (Vue) {
        Vue.component('router-link', {
            props: {
                to: String
            },
            render (h) {
                return h('a', {
                    attrs: {
                        href: this.to
                    },
                    on: {
                        click: this.clickHandler
                    }
                }, [this.$slots.default])
            },
            methods: {
                clickHandler (e) {
                    history.pushState({}, '', '#' + this.to)
                    this.$router.data.current = this.to
                    e.preventDefault()
                }
            }
        })

        const _this = this
        Vue.component('router-view', {
            render (h) {
                let component = _this.routeMap[_this.data.current]
                if (component === undefined) {
                    component = _this.routeMap['*']
                }
                return h(component)
            }
        })
    }

    initEvent () {
        if (this.options.mode === 'hash') {
            window.addEventListener("hashchange", () => {
                let newHash = window.location.hash
                this.data.current = newHash.substr(1)
            });
        } else {
            window.addEventListener('popstate', () => {
                this.data.current = window.location.pathname
            })
        }
    }
}